Ethylene polymers are conventionally used in a lot of fields, for example, used in extrusion molded articles such as films, sheets and the like. Extrusion molded articles are required to be excellent in molding processability controlled by extrusion torque, melt tension and the like, and further, required to be odorless and no to deteriorate taste of food contained in a package thereof.
A film of ethylene polymer or a composition containing ethylene polymer is usually produced by a flat (T-die) molding process or tubular molding process. While, in a tubular molding process, a temperature of a melted resin at die gap of the tubular die is usually between 180° C. and 220° C., a temperature of a melted resin at die gap of the T-die is usually between 220° C. and 260° C. in a T-die molding process due to a large pressure loss at the die.
Such high temperature at die gap causes a generation of order of film resulting from oxidizing resin, a increase of number of gels (fish-eyes) resulting from thermal degradation or cross-linkage of resin, and a staining of a molding machine resulting from accumulation of the oxidized resin.
For example, Japanese Patent Application No. 10-329195A describes a method of molding a specific ethylene polymer or a resin composition containing the specific ethylene polymer into a film at low temperature. This method may not necessarily satisfy the requirements regarding the balance between their processability and odorless or free from deteriorating taste of food contained in a package of the extruded molded article thereof, and there has been desired further improvement.
For example, Japanese Patent Application No. 4-213309A describes an ethylene copolymers comprising a repeating unit derived from ethylene and a repeating unit derived from an α-olefin having 3 to 20 carbon atoms, wherein the density is from 0.86 to 0.95 g/cm3, MFR is from 0.001 to 50 g/10 minutes, the melt tension and MFR satisfy a specific relation, and the temperature at the position of the maximum peak of a heat absorption curve measured by DSC, and the density satisfy a specific relation, as an example of ethylene copolymers excellent in melt tension and having narrow composition distribution.
The above-mentioned ethylene copolymers described in JP. 4-213309A has high melt tension, however, they may not necessarily satisfy the requirements regarding the balance between their processability and odorless or free from deteriorating taste of food contained in a package of the extruded molded article thereof.
Therefore, there has been desired further improvement in the extrusion molding processability of an ethylene copolymer and a quality of odorless or free from deteriorating taste of food contained in a package of the extruded molded article of the ethylene copolymer.
The object of the present invention is to provide a method for producing a film excellent in a quality of odorless or free from deteriorating taste of food contained in a package of the extruded molded article by using an ethylene-α-olefin copolymer excellent in extrusion molding processability. Further, the object of the present invention is to provide a film containing smaller amount of additives conventionally used by using an ethylene-α-olefin copolymer excellent in extrusion molding processability.